The invention relates to improvements in the papermaking field, and more particularly to an improved method and apparatus for cleaning of papermaking pulp utilizing a hydrocyclone.
An important field of use for centrifugal separators is in the purifying of paper stock wherein wood pulp fibers are suspended in a water solution. In the operation of a centrifugal separator or hydrocyclone, the solution of pulp is directed into the hydrocyclone and the particles are separated in categories based on physical properties. The pulp solution is directed tangentially into the hydrocyclone chamber where, under the influence of centrifugal force, the particles are separated so that reject particles of a specific weight greater than the pulp, such as bark, shives, nodules, sand, ink specks, and the like are thrown outwardly and will pass downwardly through a reject opening at the base of the hydrocyclone chamber. The acceptable fraction which is the wood pulp fiber will pass outwardly through an opening at the top center of the hydrocyclone chamber. In other hydrocyclone type cleaners, lightweight particles, that is particles having specific weights less than the pulp, can be separated using the same principles.
Typically in commercial installations for the high efficiency removal of debris in paper stock, a plurality of hydrocyclone cleaners are connected in cleaner banks to process a substantial volume of paper stock. The hydrocyclone centrifugal cleaners may be used in a batch dump operation or a continuous operation. In each operation, the cleaner must be efficient and highly effective in removing the particles of contaminants, either heavyweight or lightweight.
Typically, with an installed cleaning system, there is limited capability to adjust either capacity or cleaning efficiency without changing the type or number of installed cleaners. Generally, the only means presently available is to adjust the consistency of the stock supplied either up or down and/or to adjust the operating pressures of the system. Raising the operating consistency yields a higher tonnage through the system but will lower the cleaning efficiency. Conversely, lowering the stock consistency can increase the cleaning efficiency but will lower the system output unless additional cleaners are added to the system. Running the cleaners at a higher pressure drop will raise the capacity, but the effect on cleaning efficiency can be positive or negative, depending on the specifics of the hydrocyclone and the contaminant involved.
Hydrocyclone geometry affects both the capacity and efficiency of the hydrocyclone. The limiting factors are the basic cleaner diameter and the ratio of the inlet orifice size and the overflow or vortex finder size to the cleaner's diameter. Therefore, system changes can be made without altering stock consistency or system pressures; however, previously geometric charges to the cleaners required substantial systems downtime and expense.
A feature of the present invention is to provide an improved apparatus and method for the cleaning of pulp utilizing a hydrocyclone for the removal of undesirable particles.
A further feature of the invention is to provide an improved cleaning system using hydrocyclones for the cleaning of papermaking pulp wherein the performance of the cleaner can be readily affected by adjusting the inlet orifice and vortex finder diameters.
A still further feature of the invention is to provide a hydrocyclone cleaning system which is field adjustable to obtain a more versatile system to accommodate changing mill requirements and wherein there is a capability to adjust either capacity or cleaning efficiency without changing the number or type of installed hydrocyclone cleaners.